While this may not come as a surprise to anyone it seems Mozilla Firefox has no plans to develop a browser for Windows 10 Mobile. In response to a question Mozilla’s Communication Manager says,
Mozilla has no current plans to develop Firefox for Windows 10 Mobile
And they even mention that this statement can be attributed to a “Mozilla Spokesperson” if needed. Microsoft Edge is the native browser on windows 10 Mobile and it works really well. But Firefox desktop browser has been the browser of choice on Windows for many. So perhaps it could have been a great option on Mobile too. Windows 10 Mobile has some good 3rd party browsers in UC Browser, Opera Mini already.